[PATCH v1 2/2] ACPI: bus: Avoid using CPPC if not supported by firmware

[Rafael J. Wysocki]

From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>

If the platform firmware indicates that it does not support CPPC by
clearing the OSC_SB_CPC_SUPPORT and OSC_SB_CPCV2_SUPPORT bits in the
platform _OSC capabilities mask, avoid attempting to evaluate _CPC
which may fail in that case.

Because the OSC_SB_CPC_SUPPORT and OSC_SB_CPCV2_SUPPORT bits are only
added to the supported platform capabilities mask on x86, when
X86_FEATURE_HWP is supported, allow _CPC to be evaluated regardless
in the other cases.

Link: https://lore.kernel.org/linux-acpi/CAJZ5v0i=ecAksq0TV+iLVObm-=fUfdqPABzzkgm9K6KxO1ZCcg@xxxxxxxxxxxxxx
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
---
 drivers/acpi/bus.c       |    8 ++++++++
 drivers/acpi/cppc_acpi.c |    3 +++
 include/linux/acpi.h     |    1 +
 3 files changed, 12 insertions(+)

Index: linux-pm/drivers/acpi/bus.c
===================================================================
--- linux-pm.orig/drivers/acpi/bus.c
+++ linux-pm/drivers/acpi/bus.c
@@ -284,6 +284,8 @@ EXPORT_SYMBOL_GPL(osc_pc_lpi_support_con
 bool osc_sb_native_usb4_support_confirmed;
 EXPORT_SYMBOL_GPL(osc_sb_native_usb4_support_confirmed);
 
+bool osc_sb_cppc_not_supported;
+
 static u8 sb_uuid_str[] = "0811B06E-4A27-44F9-8D60-3CBBC22E7B48";
 static void acpi_bus_osc_negotiate_platform_control(void)
 {
@@ -339,6 +341,12 @@ static void acpi_bus_osc_negotiate_platf
 		return;
 	}
 
+#ifdef CONFIG_X86
+	if (boot_cpu_has(X86_FEATURE_HWP))
+		osc_sb_cppc_not_supported = !(capbuf_ret[OSC_SUPPORT_DWORD] &
+				(OSC_SB_CPC_SUPPORT | OSC_SB_CPCV2_SUPPORT));
+#endif
+
 	/*
 	 * Now run _OSC again with query flag clear and with the caps
 	 * supported by both the OS and the platform.
Index: linux-pm/drivers/acpi/cppc_acpi.c
===================================================================
--- linux-pm.orig/drivers/acpi/cppc_acpi.c
+++ linux-pm/drivers/acpi/cppc_acpi.c
@@ -656,6 +656,9 @@ int acpi_cppc_processor_probe(struct acp
 	acpi_status status;
 	int ret = -EFAULT;
 
+	if (osc_sb_cppc_not_supported)
+		return -ENODEV;
+
 	/* Parse the ACPI _CPC table for this CPU. */
 	status = acpi_evaluate_object_typed(handle, "_CPC", NULL, &output,
 			ACPI_TYPE_PACKAGE);
Index: linux-pm/include/linux/acpi.h
===================================================================
--- linux-pm.orig/include/linux/acpi.h
+++ linux-pm/include/linux/acpi.h
@@ -580,6 +580,7 @@ acpi_status acpi_run_osc(acpi_handle han
 extern bool osc_sb_apei_support_acked;
 extern bool osc_pc_lpi_support_confirmed;
 extern bool osc_sb_native_usb4_support_confirmed;
+extern bool osc_sb_cppc_not_supported;
 
 /* USB4 Capabilities */
 #define OSC_USB_USB3_TUNNELING			0x00000001